Resolving Greece's debt problems will require a combination of measures but should not include any change to the principal amount it owes, the European Union's top economic official said on Thursday.

"The solution will be a combination of various elements, one is not enough. But it is essential that the principal not be touched. There is a strict unanimity on this within the eurozone,» EU Economic and Monetary Affairs Commissioner Olli Rehn said.

Eurozone finance ministers will attempt to close Greece's financing gap to 2014 when they meet again in Brussels next Tuesday, instead of finding a solution for as long as 2020, a senior euro zone source told Reuters on Wednesday.

Handelsblatt, quoting European Union diplomats, said the amount need to cover the gap could be realized by lowering interest rates on outstanding debt as well as extending maturities on loans. [Reuters]